1. Field of the Invention
This invention relates to a non-reducible dielectric ceramic composition and, more particularly, to a non-reducible dielectric ceramic composition used for a monolithic ceramic capacitor and the like.
2. Description of the Prior Art
In general, a monolithic ceramic capacitor has been fablicated by first preparing dielectric ceramic green films with a conducting ink for internal electrodes printed in the designed pattern thereon. A dielectric ceramic material, for example, such as BaTiO.sub.3 system ceramic material is used for the dielectric ceramic green films. The several printed dielectric ceramic green films are stacked one on another and heat-pressed, and, finally, fired to produce monolithic ceramic capacitor units in a natural atmosphere from 1250.degree. to 1350.degree. C. Thus obtained monolithic ceramic capacitor units are finished by providing external electrode on end surface of the units for connecting to the internal electrodes.
Thus, the material for internal electrode is required to meet the following condition.
(a) It must not melt or evaporate at a sintering temperature of the dielectric ceramic materials.
(b) It must not oxidize or react with dielectric ceramic materials even if the sintering is carried out under oxidable atmosphere at high temperature.
As the electrode materials for internal electrode of monolithic ceramic capacitor, it is required to use a noble metal such as, for example, platinum, gold, palladium or alloy thereof.
However, these electrode materials having excellent characteristics are expensive. Therefore, the cost of the electrode material occupies from 30 to 70% of the total production cost of manufacturing monolithic ceramic capacitor.
Substitution of expensive materials for inexpensive base metals such as Ni, Fe, Co, W, Mo is known. These metals, however, are oxidized when fired at oxidizable high temperature and not usable for internal electrode. Therefore, it is required to develop a dielectric ceramic material which meets such a requirement that it is never reduced to a semiconductive material even when fired in a neutral or reducing atmosphere with base metals for internal electrode materials.
In order to satisfy this requirement, Japanese Patent Publication No. 42588/82 discloses the dielectric ceramic composition having large mole ratio of Ba site to Ti site compared with stoichiometric ratio of barium titanate solid solution. The dielectric ceramic composition has a superior characteristics even if fired in a reducing atmosphere, thus making it possible to use a base metal as material for internal electrode of monolithic ceramic capacitor.
In recent years, miniaturization of electronic components has rapidly progressed with the development in electronics and miniaturization of monolithic ceramic capacitor also become realized. A method of miniaturization of monolithic ceramic capacitor known as follows: Firstly, it is to use a material having large dielectric constant. Secondly it is to use a thin film of dielectric ceramic layer. However, the large dielectric constant material has a large grain size. Using thus large dielectric constant material, the number of grains in the dielectric film is decreased, and the reliability of monolithic ceramic capacitor is declined.